The present invention relates to the field of placing fill materials into the vias or holes of an electronic substrate.
A common structure in various electronics packages, such as laminate packages, wired circuit boards, ceramic substrates, and hybrid circuits, is a via or hole. A via or hole is a vertical opening which can be filled with conducting material used to connect circuits on various layers of a substrate or electronics packages to one another. Holes in certain devices may connect to a semi-conducting substrate. A hole generally starts as an empty cylindrical opening in an electronics package which is formed by drilling. The hole is then plated with an electrical conductor such as copper or tin. Plating may be done over the entire panel or device, or may be done with a pattern, dot, or button feature. The plating process results in a hole that is an opening with a plated, electrically conductive layer on the inner surface of the opening. Plating may also result in plating all or part of the surface of the device. Plating of the hole provides the primary electrical contact at the various layers within the device. The following step is to fill the hole with an electrically conductive, thermally conductive or nonconductive paste. The reasons for filling the hole after plating include providing a secondary or fail safe electrical connection, to provide structural integrity, to prevent chemical process entrapment from down-line operations, or to provide thermal conductivity to remove heat from the inner circuit layers of the resulting device. Another reason is that filling the hole also controls the breaking of electrical connections formed when the plate or finished electrical device thermally cycles between operating temperatures and non-operating temperatures.
Various methods relating to hole filling are discussed in pending U.S. patent application Ser. Nos. 09/752,629 and 09/752,503 which are directed to devices and methods for delivering a fill material using a delivery system that includes a pressurized supply of fill material and a pressure head attached to the pressurized supply of fill material.
The present invention is directed to a filling system includes a pressurized source of fill material and a pressure fill head wherein the fill head also includes a heating element positioned so as to transfer heat to fill material passing through the fill head. A method of filling holes using a fill material passing through a pressure fill head includes the steps of causing fill material to enter the fill head, modifying the viscosity of the fill material while it is within the fill head, and causing the modified viscosity fill material to exit the fill head and enter at least one hole.
Incorporation of a heating element into a pressure fill head may involve including a heating element that converts electrical energy into heat as part of the fill head, and/or pumping a heated material through a radiator that is part of the fill head.
Various objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the invention, along with the accompanying drawings in which like numerals represent like components.